Impact wrenches and other impact tools may be used to apply torque to fasteners and secure those fasteners in a variety of applications and industries. Impact wrenches typically include a rotating mass or hammer that strikes an anvil to rotate an output shaft. A socket sized to engage a fastener (e.g., bolt, screw, nut, etc.) may be formed on the output shaft, but, typically, the socket is an accessory that may be attached and detached from the output shaft. Rather than applying a constant torque when the socket is attached to a fastener, an impact wrench applies torque with each strike of the hammer.
A socket typically includes a polygonal recess for receiving a correspondingly shaped head of the fastener. The engagement between the socket and the head of the fastener creates a spring effect between those components. Another spring effect is created by the engagement between the socket and the output shaft of the impact wrench. As used herein, the term “spring effect” refers to a mechanical property that reduces the efficiency of a kinetic energy transfer. The spring effects created by the interaction between the fastener, the socket, and the output shaft of the impact wrench may diminish the amount of kinetic energy transferred from the impact wrench to the fastener and therefore diminish the amount of torque delivered to the fastener.
The mechanical system formed by the fastener, the socket, and the output shaft of the impact wrench may be represented as a single-mass oscillator system. While the system is a rotary system, the system may be illustrated as a simplified linear system such as the one shown in FIG. 6. That system includes a typical socket, fastener, and impact wrench. As shown in FIG. 6, the mass moment of inertia of the output shaft of the impact wrench is designated by m1, while the fastener is represented by ground. To illustrate a typical spring effect introduced by the connection between the output shaft and the socket, that connection is designated k1 in FIG. 6. Similarly, the connection between the socket and the fastener is designated by k2 to show the spring rate typically created by that connection. In the typical system shown in FIG. 6, the combined spring rate of k1 and k2 converts a portion of the kinetic energy created by the impact wrench into potential energy, thereby diminishing the kinetic energy transferred from the impact wrench to the fastener and reducing the amount of torque delivered to the fastener.